Checking engine temperature sender: VW 1.9 D (AEF)

Special tools, testers and auxiliary items

Fault reader V.A.G 1551 or vehicle system tester V.A.G 1552 with cable V.A.G 1551/3
Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
Adapter set V.A.G 1594
Current flow diagram

Test sequence

Connect fault reader V.A.G 1551 (V.A.G 1552) and with the "Address word" 41 select the Diesel pump electronics control unit. When doing this the engine should be idling.
(Connecting fault reader and selecting engine electronics control unit => Page
01-3
.)

Rapid data transfer
HELP
Select function XX
Indicated on display:

Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.

Read measured value block
HELP
Input display group number XX
Indicated on display:

Press keys 0 and 1 for "Display group number 01" and confirm entry with Q key.

Read measured value block
1
⇒
1
2
3
4
Indicated on display:
(1...4 = Display zones)

Read coolant temperature value in display zone 3.

Display · Cause · Continuation of check
-20 °C · Open circuit or short to positive · => Page 23-48
120 °C · Short to earth · => Page 23-50
Approx. coolant temperature1) · --- · Only if spora- / dic faults / have been / detected:2) / => Page 23-51

1)
If a temperature is displayed which deviates greatly from the ambient temperature of the sender, check sender wiring for transfer resistances.

2)
Check is only possible when the engine is cold.

Continuation of check when display = -20 °C:

Pull 4 pin connector -1- off engine temperature sender (G27) -2-.
Bridge connector contacts 1+3 using aux. cables from V.A.G 1594 and observe display.

Display 120 °C:

Press ⇒key.
Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
Switch off ignition.
Renew engine temperature sender -2-.

Display -20 ° C:

Press ⇒key.
Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
Switch off ignition.
Check wire between automatic glow period control unit (J179) and 4 pin connector contact 3 for open circuit according to current flow diagram.
Wire resistance: Max. 1.5 ω
Check wiring additionally for short circuit to battery positive.
Specification: ∞ω
Check wire to 4 pin connector contact 1 for open circuit according to current flow diagram.
Wire resistance: Max. 1.5 ω

If no fault in wire is detected:

Replace automatic glow period control unit (J179).

Continuation of check when display = 120 °C:

Pull 4 pin connector -1- off engine temperature sender (G27) -2-.

Display -20 ° C:

Press ⇒key.
Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
Switch off ignition.
Replace engine temperature sender -2-.

Display 120 °C:

Press ⇒key.
Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
Switch off ignition.
Check wire between automatic glow period control unit (J179) and 4 pin connector contact 3 for short to wire contact 1 and to vehicle earth, according to current flow diagram.
Specification: ∞ω

If no fault in wire is detected:

Replace automatic glow period control unit (J179).

Continuation of check when display = coolant temperature:

Functional check of sender

With engine running observe coolant temperature value in display zone 3. The temperature figure must
increase uniformly and without interruption.

Notes:

If the display on fault reader jumps by 2...5 °C, it is a control unit fault and not caused by a defective sender.

If irregular engine running occurs in certain temperature ranges and the temperature figure does not increase without interruption, the temperature signal is temporarily interrupted and the sender must be renewed.

Press ⇒key.
Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.